Motor-control system



E. R. CARICHOFF.

MOTOR CONTROL SYSTEM.

APPLICATION FILED MAY 6. 1918.

1,337,040. Patented Apr. 13,1920.

Inventor" Eugene Rfiarichoff,

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His flttofney UNITED STATES P ATENT OFFICE.

EUGENE R. CARICHOFF, 0F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MOTOR-CONTROL SYSTEM.

Application filed May 6, 1918.

To all whom it may concern:

Be it known that I, EUGENE R. CARIOHOFF, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Motor Control Systems, of which the following is a specification.

My invention relates to the control of electric circuits by means of electromagnetic switches and has for its object the provision of improved means whereby an electric circuit may be controlled in a simple, reliable and efiicient manner.

My invention relates more specifically to the control of electric motor circuits by electromagnetic switches, one of the objects being to provide an improved device of this character which. will effect the automatic starting of the motor under the control of the motor current. In the operation of electric motors it is common to both start the motor and control its speed by means of a resistance which is 'cut' in and out of circuit. Every time a section of resistance is cut out, the current temporarily rises above normal value. The increase in speed which is caused by the cutting out of the section of resistance immediately reduces the current. During the starting of the motor, therefore, there is a temporary rush of current'for each section of resistance cut out. These sections are frequently cut out of circuit by electromagnetic switches which ioperate automatically in succession. In order to prevent these switches from operating too rapidly and increasing the current beyond a safe value, various means have been devised. An ideal switch for this purpose is one containing a winding which carries the motor current and a switch member controlled thereby for cutting out the re sistance, the arrangement being such that the switch member will not be operated to cut out the resistance until the current has fallen to a predetermined value and will assume an open position when the winding is 'deenergized. A switch of this character was invented by Walter O. Lum and forms the subject matter of an application, Serial No. 611,151, filed February 27, 1911, assigned to the same assignee as this application.

In my previous application, Serial No. 870,807, filed November 7, 1914., (Patent #1,280,661, October 8, 1918,) I have dis- Specification of Letters Patent.

Patented Apr. 13, 1920.

Serial No. 232,726.

closed an electromagnetic switch for controlling electric motor circuits, which is in the nature of an improvement upon the switch covered by the above mentioned ap plication. The switch covered by my previous application involves the use of an auxiliarymember which, upon the energization of the magentizing winding, places a spring under strain tending to close the switch, the switch being normally held open due to the energization by the winding while the current is high. When the current drops to the predetermined value the force of the spring overcomes the holding-out force and the switch closes and is held closed. magnetically. In carrying out my present invention I utilize an agency external to the switch itself for giving the switch a closing tendency. In one form of my invention I employ a plurality of switches, the closure of one of which places a spring under strain and gives the succeeding switch a tendency to close so that the switch will close when the current in the winding drops to the predetermined value. The arrangement is simple and in certain applications might be preferable to my earlier form. The specific features of novelty will appear in the course of the following specification in which I have shown my invention embodied in concrete form for purposes of illustration.

In the accompanying drawing illustrating my invention diagrammatically, A represents the armature and F the series field of the electric motor to be controlled. A, B and C represent electromagnetic switches for controlling the motor circuit. As shown, switch A is an electromagnetic switch for closing the electric motor circuit, while switches B and C out out sections of resistance R and B respectively. Switch A may be of any ordinary type of electromagnetic switch provided with a shunt winding 10 for operating the switch arm 11, the winding being controlled by a manually operated switch 12. The switches B and G are alike, each consisting of a magnetizing winding 13 and a switch arm 14, pivoted at 15 to the magnet frame 16. As shown, this magnet frame comprises members 17 and 18 arranged to form two pole pieces 1.9 and 20 between which the end of the switch lever 14; moves. The arrangement is such that when the winding 13 is energized above a predetermined value, the switch member which is normally in open position against a non-magnetic stop in the pole piece 20 will be held by that pole piece in its open position; whereas, when the switch is in its closed position it is held closed by the pole piece 19. In order to give this switch member 14 a tendency to close so that it will overcome the magnetic holding-out force when the current in the winding 13 drops to a predetermined value, I apply a spring pressure thereto upon the closing of the switch A. As shown in the drawing, this is accomplished by connecting the two switch levers through a spring 21. For purposes of illustration I have shown the spring 21 connected between the two rods 22 and 23, connected respectively to switch arms 11 and 14. The rod 22 has a lost motion connection with the switch arm 11 as shown to permit the switch contacts to touch and close the motor circuit before the spring is strained. This insures that the switch arm 14 will be held in open position by magnetic force due to the energization of the winding 13 against the tension of the spring. After the contacts touch there is a wiping action due to the spring pressed pivoted contact 24 and it is this final movement of the switch arm 11 that strains the spring 21. In like manner I connect the switch levers of the two switches B and G by a spring 25 so that when the switch 13 closes it will give the movable member of switch C a tendency to close.

As thus constructed and arranged the operation of my arrangement is as follows: To start the motor the manually operated switch 12 is closed, whereupon the contactor A closes and completes the motor circuit from line through the switch member 11, through the winding 13 of switch B, resistance R, winding of switch C, resistance B, through the motor to the other side of the line. The closing of the switch 11 places the spring 21 under tension, but the rush of current holds the switch member 14 in open position. As the motor speeds up the current will decrease and when it reaches a predetermined value the closing forces, which will be the force of the spring supplemented by the magnetic pull at the pole piece 19, will overcome the holding-out force at the pole piece 17 and the switch B will close and be held closed by the pole piece 19. The closing of switch B short circuits resistance R to cause a second rush of current and also places the spring 25 under tension so that when the current drops to the predetermined value the switch C will close and place the motor across the line. Upon the opening of switch 12 all of electromagnetic switches will open and the motor will stop.

While I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto as various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A motor control system comprising a plurality of normally open electromagnetic switches each having a winding energized by the motor current and arranged to hold it in open position when the winding is energized above a predetermined value and means whereby one switch in closing directly applies a force to another switch which opposes the holding-out force of the winding to cause the switch to close when the current in the winding drops to a predetermined value.

2. A motor control system comprising a plurality of normally open electromagnetic switches each having a winding energized by the motor current arranged to hold the switch member in a closed position and to hold it in open position when the winding is energized above a predetermined value and means whereby the closure of one switch applies a constant force to another switch which opposes the holding-out force of the winding to cause the switch to close when the current in the winding drops to a predetermined value.

3. The combination with an electric motor of means for controlling the same comprising a normally open electromagnetic switch having a winding energized by the motor current and arranged to hold the switch member in a closed position and to hold it in open position when the winding is energized above a predetermined value and means independent of the winding for giving the switch a closing tendency which will overcome the holding-out force of the winding when the current in the winding drops to a predetermined value.

4. The combination of an electric motor of means for controlling the same comprising a normally open electromagnetic switch having a winding energized by the motor current and arranged to hold it in open position when the winding is energized above a predetermined value, a second switch for controlling the motor circuit and a mechanical connection between the switches whereby the closure of said second switch directly applies a force to the magnetic switch which opposes the holding-out force of the winding to cause the switch to close when the current in the winding drops to a redetermined value.

5. e combination with an electric motor of means for controlling the same comprising a normally open electromagnetic switch having a winding energized by the motor current and arranged to hold the switch member in a closed position and to hold it in open position when the winding is energized above a predetermined value, a second switch for controlling the motor circuit and means whereby the closure of said second switch applies force to the magnetic switch which opposes the holding-out force of the winding to cause the switch to close when the current in the winding drops to a predetermined value.

6. The combination with an electric motor of means for controlling the same comprising a normally open electromagnetic switch having a winding energized by the motor current and arranged to hold the switch member in a closed position and to hold it in open position when the winding is energized above a predetermined value, a spring associated with the movable member of said switch and means independent of the winding for placing said spring under strain to give the switch a closing tendency which will overcome the holding-out force of the winding when the current in the winding drops to the predetermined value.

7. The combination with an electric motor of means for controlling the same comprising a normally open electromagnetic switch having a winding energized by the motor current and arranged to hold the switch member in a closed position and to hold it in open position when the winding is energized above a predetermined value, a spring associated with the movable member of said switch, a second switch for controlling the motor circuit and means whereby the closure of said second switch places the spring under strain to give the movable member of the electromagnetic switch a closing tendency which will overcome the holding-out force of the winding when the current in the winding drops to the predetermined value.

8. A motor control system comprising a plurality of normally open electromagnetic switches each having a winding energized by the motor current and arranged to hold it in open position when the winding is energized above a predetermined value, and a spring connection between the movable members of said switches whereby the closure of one switch gives another switch a closing tendency which will overcome the holding-out force of the winding when the current in the winding drops to the predetermined value.

In witness whereof I have hereunto set my hand this 4th day of May, 1918.

EUGENE R. CARIGHOFF. 

